Transmission on a Cell

ABSTRACT

Methods and apparatus are provided. In an example aspect, a method performed by a wireless device is provided. The method comprises receiving an indication that data scheduled to be transmitted from the wireless device to a network node on a first cell using unlicensed spectrum should be transmitted on a second cell different to the first cell, and transmitting the data on the second cell.

TECHNICAL FIELD

Examples of the present disclosure relate to a transmission on a cell, for example a cell in unlicensed or licensed spectrum.

BACKGROUND

3GPP radio technologies, such as for example Long Term Evolution (LTE) or New Radio (NR), may be used in licensed spectrum. Initiatives like Licence Assisted Access (LAA), MulteFire and NR-U are solutions to use LTE and NR in unlicensed spectrum. Using unlicensed spectrum may increase the overall capacity of a network if used in parallel to licensed spectrum.

Using unlicensed spectrum, such as for example industrial, scientific and medical (ISM) radio bands, may require the use of Clear Channel Assessment (CCA) or Listen Before Talk (LBT) Medium Access Control (MAC) schemes, in which a transmitter first senses that the transmission medium is free before using it for transmissions.

SUMMARY

One aspect of the present disclosure provides a method performed by a wireless device. The method comprises receiving an indication that data scheduled to be transmitted from the wireless device to a network node on a first cell using unlicensed spectrum should be transmitted on a second cell different to the first cell, and transmitting the data on the second cell.

Another aspect of the present disclosure provides a method performed by a network node. The method comprises determining that a data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received, and sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell different to the first cell.

A further aspect of the present disclosure provides apparatus comprising a processor and a memory. The memory contains instructions executable by the processor such that the apparatus is operable to receive an indication that data scheduled to be transmitted from the wireless device to a network node on a first cell using unlicensed spectrum should be transmitted on a second cell different to the first cell, and transmit the data on the second cell.

A still further aspect of the present disclosure provides apparatus comprising a processor and a memory. The memory contains instructions executable by the processor such that the apparatus is operable to determine that a data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received, and send an indication to the wireless device to cause the wireless device to transmit the data on a second cell different to the first cell.

An additional aspect of the present disclosure provides apparatus configured to receive an indication that a data scheduled to be transmitted from the wireless device to a network node on a first cell using unlicensed spectrum should be transmitted on a second cell different to the first cell, and transmit the data on the second cell.

Another aspect of the present disclosure provides apparatus configured to determine that a data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received, and send an indication to the wireless device to cause the wireless device to transmit the data on a second cell different to the first cell.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of examples of the present disclosure, and to show more clearly how the examples may be carried into effect, reference will now be made, by way of example only, to the following drawings in which:

FIG. 1 is a flow chart of an example of a method performed by a wireless device;

FIG. 2 is a flow chart of an example of a method performed by a network node;

FIG. 3 is a schematic of an example of apparatus;

FIG. 4 is a schematic of an example of apparatus;

FIG. 5 illustrates an example of communications between a wireless device and a network in an example; and

FIG. 6 illustrates another example of communications between a wireless device and a network in an example.

DETAILED DESCRIPTION

The following sets forth specific details, such as particular embodiments or examples for purposes of explanation and not limitation. It will be appreciated by one skilled in the art that other examples may be employed apart from these specific details. In some instances, detailed descriptions of well-known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g., analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc.) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, where appropriate the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analogue) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions.

Allowing networks to operate in shared spectrum (or unlicensed spectrum) is an approach that may increase network capacity. Although unlicensed spectrum does not match the qualities of licensed spectrum, for example in terms of reliability, bandwidth, availability and/or latency, solutions that allow an efficient use of unlicensed spectrum as a complement to licensed spectrum (such as, for example, solutions provided herein) have the potential to provide increased capacity while mitigating or avoiding at least some of the drawbacks. Some features in a network technology, such as for example LTE or NR, may need to be adapted to comply with the special characteristics of the unlicensed band as well as also different regulations. When operating in unlicensed spectrum, a device may be required to sense the medium as free before transmitting. This operation is often referred to as Listen

Before Talk (LBT). Sensing may be performed in a particular channel (corresponding to a defined carrier frequency) and over a predefined bandwidth. For example, in the 5 GHz band, the sensing is performed over 20 MHz bandwidth. Examples of LBT procedures are described in standards EN 301.893, 5 GHz RLAN, Harmonized standard covering the essential requirements of article 3.2 of Directive 2014/53/EU, which is incorporated herein by reference.

Using unlicensed spectrum and/or Listen Before Talk (LBT) procedures can in some cases cause problems for applications that have a fixed upper bound on the latency of related communications. Additionally or alternatively, applications supporting high reliability and deterministic latency, such as for example URLLC (Ultra Reliable Low-Latency Communications) or HRLLC (Highly Reliable Low-Latency Communications) schemes, may not be suitable for unlicensed spectrum use, as exclusive or guaranteed use of the unlicensed wireless spectrum or unlicensed channels is not provided. URLLC, for example, has strict requirements on transmission reliability and latency, i.e., 99.9999% reliability within 1 ms one-way latency. However, it is not known at a particular time whether unlicensed spectrum is occupied (e.g. by other radio technologies such as Wi-Fi) or can be used for transmissions, and a transmitter may need to wait for a channel in unlicensed spectrum to be free (e.g. no usage of the channel is detected) before it can begin transmissions. Hence, the latency of communications using that channel cannot easily be predicted or controlled, and the reliability of communications using unlicensed spectrum cannot be guaranteed.

URLLC operation has large bandwidth requirements given the need for extremely robust encoding techniques. Licensed spectrum may however be scarce and/or expensive, but nonetheless may be able to guarantee high reliability and QoS levels. Therefore, the use of unlicensed spectrum for communications (e.g. 5G or New Radio, NR, communications as well as other technologies such as LTE) or URLLC communications is considered for examples of this disclosure. It is however currently unclear how URLLC requirements and/or requirements from Time Sensitive Networking (TSN), such as reaching a deterministic low latency performance, can be achieved by operation in unlicensed shared spectrum that is primarily used for best effort services.

Examples of this disclosure may provide mechanisms to meet high reliability and/or low latency targets (e.g. for URLLC) even when unlicensed spectrum is used. Example methods propose to exploit unlicensed carriers as long as the reliability/latency targets are not compromised, and switching to licensed spectrum (or another cell on licensed spectrum) when the reliability and/or latency targets cannot be met. A network node, such as a base station (e.g. eNB or gNB) may for example initiate the switching by a wireless device or UE from unlicensed (U) to licensed (L), based on not receiving (or not successfully receiving or decoding) an expected transmission on unlicensed. In this case, the network node may cause a grant on another cell e.g. a licensed cell to be scheduled, which triggers the wireless device or UE to (re)transmit the data on the other cell or carrier. Benefits may include, for example, meeting latency and/or reliability targets by using unlicensed carriers complemented by licensed carrier or a second unlicensed carrier, and/or reducing dependency on a licensed carrier to meet latency/reliability targets.

FIG. 1 is a flow chart of an example of a method 100 performed by a wireless device such as for example a User Equipment (UE). The method 100 comprises, in step 102, receiving an indication that data scheduled to be transmitted from the wireless device to a network node on a first cell using unlicensed spectrum should be transmitted on a second cell different to the first cell. In some examples, the indication may be received on the second cell, or on another cell that uses licensed spectrum. Step 104 of the method 100 comprises transmitting the data on the second cell.

Thus, in some examples, the network (e.g. the network node, base station, or some other node in the network) may control the cell that is used by the UE for transmissions. In some examples, the first cell is a cell on unlicensed spectrum, and the second cell is a cell on licensed or unlicensed spectrum. Thus the network may for example control switching of the wireless device from using unlicensed spectrum to using licensed spectrum for the transmission. The data (or the scheduled transmission of the data) may be explicitly identified (e.g. referred to), or alternatively the data (or transmission) may not be identified (and thus for example following the indication, a certain number of transmissions may be sent on the second cell instead of the first cell and/or transmissions within a certain time period may be sent on the second cell instead of the first cell, such as for example time period T0 as illustrated in FIG. 6).

In some examples, transmitting the data on the second cell comprises transmitting the data to the network node on the second cell. The network node may be for example a base station or a destination of the transmission (e.g. a destination for data packets), or any other network node.

In some examples, transmitting the data on the second cell comprises transmitting the data to the network node using licensed spectrum. That is, for example, the cell may be a cell on licensed spectrum. In such examples, the wireless device may be guaranteed to be able to use the second cell. In some examples, the wireless device may request to use the second cell for the transmission by sending a scheduling request, e.g. to the network node or a base station associated with the second cell, and receiving a scheduling grant which schedules the wireless device to use the second cell for transmission.

Transmitting the data on the second cell may in some examples comprise transmitting the data to the network node using unlicensed spectrum. That is, for example, the wireless device may use the second unlicensed cell instead of the first unlicensed cell. The second cell may for example be unoccupied or free compared to the first cell which is occupied.

In some examples, receiving the indication comprises receiving an uplink grant for transmitting the data on the second cell. The wireless device may thus determine from the indication that the data should be transmitted on the second cell.

The method 100 may in some examples comprise stopping transmitting data on the first cell in response to receiving the indication. This may occur for example if the wireless device has already begun the transmission on the first cell. The network node may not be able to successfully receive at least part of the transmission for example due to interference or other reasons. Therefore, it may not be possible to recover the entire transmission from the point of the indication, and the wireless device may thus stop the transmission on the first cell at that point. If the data from the wireless device was partially unsuccessfully transmitted, the method 100 may comprise retransmitting the data on the second cell (e.g. starting the transmission of the data again), or continuing the transmission of the data on the second cell from the point where transmission was stopped on the first cell. In some examples, the transmission of the data on the first cell may be stopped in response to receiving a scheduling grant for the second cell. This could, therefore, be treated in some examples as an indication that the transmission of the data on the first cell has been unsuccessful. If the data from the wireless device was partially unsuccessfully transmitted, the indication may in some examples comprise a retransmission request, such as for example a HARQ retransmission request. In such examples, transmitting the data on the second cell may comprise performing a retransmission on the second cell.

The method 100 may in some examples comprise determining that the data is at least partially unsuccessfully transmitted (including for example where no data was transmitted at all, where the data was partially transmitted, or where a negative acknowledgement or other indication of unsuccessful transmission is received from the network node), and sending a notification to the network node that the data is at least partially unsuccessfully transmitted, wherein the indication may be received in response to determining that the data on the first cell is at least partially unsuccessfully transmitted. In one example of this scenario, the wireless device may determine that no data was transmitted on the first cell at all, for example due to LBT failure or failure to access the channel on the first cell. In another example, the UE may determine that only some of the data was sent. This may occur e.g. if the data transmission is discontinuous or segmented, and the wireless device was unsuccessful in gaining access to the channel for a second or subsequent time. In some examples, therefore, the transmission of the data on the first cell may be completely unsuccessful, e.g. none of the data was successfully transmitted, or the data was transmitted and/or retransmitted on the first cell after one or more LBT attempts, but could not be successfully decoded by the network node and therefore the transmission is considered (partially) unsuccessful. This may be for example due to the wireless device detecting that the first cell, or a channel on the first cell that the wireless device intends to use, is occupied, e.g. by another wireless device. This may be determined for example by determining a number of Listen Before Talk, LBT, failures or a rate of LBT failures during transmission attempts for the transmission, and determining that the number of LBT failures or rate of LBT failures meets or exceeds a threshold number or rate. Sending the notification may in some examples comprise sending the notification on the second cell or a cell using licensed spectrum.

In some examples, the indication from the network node indicates that the data has not been received by the network node on the first cell at a time scheduled for the data on the first cell or within a predetermined time of the time scheduled for the data on the first cell. Thus, for example, the network node or a base station may have expected the data from the wireless device (e.g. due to a scheduling grant or an expected periodic transmission), but it was not successfully received. This may be due to interference of the transmission, or alternatively the wireless device may not have transmitted the data at all due to e.g. the first cell or channel on the first cell being occupied. The indication may in some examples be received after a time scheduled for the transmission on the first cell.

In some examples, the transmission comprises an Ultra Reliable Low Latency Communications, URLLC, transmission. Transmitting the transmission on the second cell may in some examples be more reliable and/or have lower latency than repeatedly attempting to transmit the transmission on the first cell.

FIG. 2 is a flow chart of an example of a method 200 performed by a network node, such as for example a base station or other network node. The method comprises, in step 202, determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received. For example, this may comprise determining that data that is received is not successfully decoded, or is only partially received, or that the data or a transmission that is expected (e.g. due to a scheduling grant or a periodic transmission) is not received. The method 100 also comprises, in step 204, sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell different to the first cell. Thus, in some examples, the network node (or the network in general) may control the switching of the wireless device between using different cells, such as for example between using a cell on unlicensed spectrum to a cell on licensed spectrum. In some examples, the wireless device may be performing the method 100 described above. In some examples, the network node may subsequently receive the data from the wireless device on the second cell.

In some examples, sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell may comprise sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell using licensed spectrum. That is, the second cell is on licensed spectrum. Thus for example the data on the second cell by the wireless device may be guaranteed to be transmitted. Alternatively, the second cell may be on unlicensed spectrum, wherein the second cell has much lower channel occupancy and therefore, significantly higher probability to find a free channel or higher LBT success probability.

In some examples, the indication sent to the wireless device is an uplink grant, for example for transmitting the data on the second cell. Additionally or alternatively, the indication may be sent on the second cell to the wireless device, or may be sent on another cell in licensed spectrum.

Determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received may in some examples comprise determining that the data has at least partially not been successfully decoded, or determining that the data has not been received at all (e.g. undetected).

In some examples, determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received comprises determining that the data is at least partially unsuccessfully transmitted by the wireless device. This may be determined for example by receiving a notification from the wireless device that the data is at least partially unsuccessfully transmitted. For example, the wireless device may send this notification due to lack of success in gaining access to the channel on the first cell, e.g. one or more LBT failures. In some examples, the notification received from the wireless device may indicate the number of LBT failures or rate of LBT failures or indicates that the number of LBT failures or rate of LBT failures meets or exceeds a threshold number or rate. The notification may be received in some examples on the second cell or a cell using licensed spectrum. This may be useful if for example the reason that the wireless device sent the notification is due to failure to access the channel on the first cell.

In some examples, determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received comprises determining that the data has not been successfully received at a time scheduled for the data on the first cell or within a predetermined time of the time scheduled for the data on the first cell. For example, the data may be expected, due to e.g. an earlier scheduling grant or an expected periodic transmission from the wireless device.

In some examples, determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received comprises determining that a start of the data is received. If, for example, the data is subsequently not successfully received, e.g. due to interference or other factors, the network node may send the indication to the wireless device.

Particular examples will now be described. Some are in the context of switching from unlicensed to licensed spectrum, whereas these examples are equally applicable to switching between cells which are both on unlicensed spectrum. In some examples, if a transmission attempt on a serving cell operating in unlicensed/shared spectrum (referred to as U herein) fails or is expected to fail, or is identified by a network node (e.g. base station, gNB or eNB) as having failed, meaning e.g. that it could not be transmitted after a certain time T or the base station registers a missing transmission or is informed of a failed transmission attempt, a (re)transmission is scheduled by a network node of that data in another serving cell. In some examples, the other serving cell operates in licensed spectrum (referred to as L herein), and therefore the transmission or retransmission attempt on the other serving cell (e.g. the second cell referred to above) is unlikely to fail. Thus, for example, there is a network-initiated switch of a data transmission (e.g. uplink data transmission) from U to L (or another U cell) if the transmission attempt on the first cell is regarded as unsuccessful. If another unlicensed cell is switched to, this may be for example another unlicensed cell that is serving less traffic than the first cell.

Firstly, the network node in some examples is aware that a transmission attempt had taken place by the UE, and the transmission was not successfully received by recipient, which may be the network node, due to e.g. the transmission not being sent in the first place or due to interference or other factors. The network node may then schedule the retransmission (or the transmission if it was not sent on the first cell in the first place), e.g. on a cell in L (as further described in below paragraphs). The network node may in some examples learn or be informed of the wireless device/UE traffic pattern and predict further occurrence of the traffic. This may be particularly possible for URLLC/TSN traffic, which may be periodic with a deterministic periodicity. For those, typically periodic UL (configured) grants are provided, for which the network node can check whether transmissions took place and are successfully decodable or not. When no UE data transmission is successfully decoded the expected data transmission occurrence by the network node (or for a certain time T thereafter), the network node triggers a retransmission. Other triggers include the network node detecting transmission attempts by the wireless device but failing to decode the transmission, e.g. due to hidden node issues leading to higher interference. Alternatively, previously sent scheduling requests or buffer status reports received from the wireless device, indicating that the UE needs to transmit data, but missing subsequent transmissions of that data, may be counted as triggers to issue the (re)transmission grant (e.g. referred to as a indication above).

In another example for identifying whether a transmission on U by the wireless device was unsuccessful, the wireless device may indicate to the network node (e.g. via a licensed cell, such as for example the second cell) a LBT failure or number of LBT failures, LBT failure over period of time or LBT failure rate within a particular time period. The network node may cause retransmission on L taking into account this indication from the wireless device. This may also allow the network node to dynamically reserve licensed resources for a future potential retransmission e.g. over L. The indication can be sent over dedicated control signaling or enhancement in CSI report(s) from the wireless device towards the network periodically. The periodicity of the message may in some examples depend upon the reliability targets for an URLLC application.

In some examples, the network node triggers the (re)transmission on L of the potentially transmitted/lost data previously sent or scheduled or expected to be sent on U. This retransmission can be indicated as a special retransmission grant, e.g. indicated in downlink control information (DCI) of an uplink grant. When the wireless device receives such a grant, it stops any further transmission of the data corresponding to the transmission on U and retransmits the data on L instead. If no data transmission was attempted within a certain time before the special grant was received, the grant may be ignored by the wireless device in some examples. Thus, for example, the wireless device may consider the special grant as a command to switch cell and retransmit.

For retransmission handling on HARQ/MAC, there can be different assumptions on HARQ processes. Typically, different HARQ processes are used/defined for each cell. However, in some examples of this disclosure, the HARQ processes could also be shared between the cells on U and L, as they are intended to be used with mutual exclusion, i.e. the transmission is to be performed on U or L, or sequentially where the transmission is first attempted on U, and if unsuccessful, then further attempts are made on L. Therefore, when a retransmission request is received, if different HARQ processes are used/defined for the cells on U and L, the wireless device can copy the MAC PDU (pending/transmitted data) from the HARQ process buffer for U to the HARQ process buffer for L for transmission on L. The HARQ process buffer on U may be flushed thereafter. In the case that the same HARQ process may be used on both U and L, a HARQ retransmission may be initiated for the previously transmitted data on L, e.g. the HARQ process becomes associated with L instead of U.

FIG. 3 is a schematic of an example of apparatus 300 comprising processing circuitry 302 (e.g. one or more processors) and a memory 304 in communication with the processing circuitry 302. The memory 304 contains instructions executable by the processing circuitry 302. The apparatus 300 also comprises an interface 306 in communication with the processing circuitry 302. Although the interface 306, processing circuitry 302 and memory 304 are shown connected in series, these may alternatively be interconnected in any other way, for example via a bus.

In one embodiment, the memory 304 contains instructions executable by the processing circuitry 302 such that the apparatus 300 is operable to receive an indication that a data scheduled to be transmitted from the wireless device to a network node on a first cell using unlicensed spectrum should be transmitted on a second cell different to the first cell, and transmit the data on the second cell. In some examples, the apparatus 300 is operable to carry out the method 300 described above with reference to FIG. 1.

FIG. 4 is a schematic of an example of apparatus 400 comprising processing circuitry 402 (e.g. one or more processors) and a memory 404 in communication with the processing circuitry 402. The memory 404 contains instructions executable by the processing circuitry 402. The apparatus 400 also comprises an interface 406 in communication with the processing circuitry 402. Although the interface 406, processing circuitry 402 and memory 404 are shown connected in series, these may alternatively be interconnected in any other way, for example via a bus.

In one embodiment, the memory 404 contains instructions executable by the processing circuitry 402 such that the apparatus 400 is operable to determine that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received, and send an indication to the wireless device to cause the wireless device to transmit the data on a second cell different to the first cell. In some examples, the apparatus 400 is operable to carry out the method 400 described above with reference to FIG. 2.

FIG. 5 illustrates an example 500 of communications between a wireless device and a network in an example implementation of embodiments of this disclosure. FIG. 6 illustrates an example 600 of communications between a wireless device and a network in an example implementation of embodiments of this disclosure. In these figures, dotted lines and boxes indicate optional features of these examples.

It should be noted that the above-mentioned examples illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative examples without departing from the scope of the appended statements. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the statements below. Where the terms, “first”, “second” etc. are used they are to be understood merely as labels for the convenient identification of a particular feature. In particular, they are not to be interpreted as describing the first or the second feature of a plurality of such features (i.e. the first or second of such features to occur in time or space) unless explicitly stated otherwise. Steps in the methods disclosed herein may be carried out in any order unless expressly otherwise stated. Any reference signs in the statements shall not be construed so as to limit their scope. 

1-46. (canceled)
 47. A method performed by a network node, the method comprising: determining that data scheduled for transmission from a wireless device on a first cell using unlicensed spectrum has not been successfully received; and sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell different from the first cell.
 48. The method of claim 47, comprising receiving the data on the second cell from the wireless device.
 49. The method of claim 47, wherein sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell comprises sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell using licensed spectrum.
 50. The method of claim 47, wherein sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell comprises sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell using unlicensed spectrum.
 51. The method of claim 47, wherein sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell comprises sending an uplink grant to the wireless device.
 52. The method of claim 47, wherein sending an indication to the wireless device to cause the wireless device to transmit the data on a second cell comprises sending the indication on the second cell or a cell using licensed spectrum.
 53. The method of claim 47, wherein determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received comprises determining that the data has at least partially not been successfully decoded.
 54. The method of claim 47, wherein determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received comprises determining that the data is at least partially unsuccessfully transmitted by the wireless device.
 55. The method of claim 54, wherein determining that the data is at least partially unsuccessfully transmitted by the wireless device comprises receiving a notification from the wireless device that the data is at least partially unsuccessfully transmitted.
 56. The method of claim 55, wherein determining that the data is at least partially unsuccessfully transmitted comprises determining a number of Listen Before Talk (LBT) failures or a rate of LBT failures during transmission attempts for the data by the wireless device, and determining that the number of LBT failures or rate of LBT failures meets or exceeds a threshold number or rate.
 57. The method of claim 56, wherein the notification received from the wireless device indicates the number of LBT failures or rate of LBT failures or indicates that the number of LBT failures or rate of LBT failures meets or exceeds a threshold number or rate.
 58. The method of claim 54, wherein receiving the notification comprises receiving the notification on the second cell or a cell using licensed spectrum.
 59. The method of claim 54, wherein determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received comprises determining that the data has not been successfully received at a time scheduled for the data on the first cell or within a predetermined time of the time scheduled for the data on the first cell.
 60. The method of claim 47, wherein determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received comprises determining that a periodic transmission from the wireless device has not been successfully received.
 61. The method of claim 47, wherein determining that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received comprises determining that a start of the data is received.
 62. The method of claim 47, wherein sending an indication comprises sending the indication on the second cell or a cell using licensed spectrum.
 63. A non-transitory computer-readable medium comprising, stored thereupon, a computer program configured for execution by a processor in a network node and configured to cause the network node to: determine that data scheduled for transmission from a wireless device on a first cell using unlicensed spectrum has not been successfully received; and send an indication to the wireless device to cause the wireless device to transmit the data on a second cell different from the first cell.
 64. A network node comprising a processor and a memory, the memory containing instructions executable by the processor such that the apparatus is operable to: determine that data scheduled to be transmitted from a wireless device on a first cell using unlicensed spectrum has not been successfully received; and send an indication to the wireless device to cause the wireless device to transmit the data on a second cell different to the first cell. 